Step 1:
The first step to converting 21243.578 to a fraction is to re-write 21243.578 in the form p/q where p and q are both positive integers. To start with, 21243.578 can be written as simply 21243.578/1 to technically be written as a fraction.
Step 2:
Next, we will count the number of fractional digits after the decimal point in 21243.578, which in this case is 3. For however many digits after the decimal point there are, we will multiply the numerator and denominator of 21243.578/1 each by 10 to the power of that many digits. So, in this case, we will multiply the numerator and denominator of 21243.578/1 each by 1000:
Step 3:
Now the last step is to simplify the fraction (if possible) by finding similar factors and cancelling them out, which leads to the following answer for 21243.578 as a fraction:
148705/7 / 1